The invention relates to a device for determining a complete track number or address(s) of a track which forms part of a set of tracks present on a disc-shaped record carrier, said set consisting of (n) groups of (s.sub.g) tracks, the record carrier being divided into alternating sectors with groups of data tracks and sectors with groups of servo tracks, each track having per group of servo tracks its own identification code which includes a number of the track within the group and which can be read by a transducer device provided on a positioning member.
A device of this kind is used in disc memories in which one or more discs provided with or made of a storage material (for example, magnetic, optical, ceramic) are used for the writing, storage and reading of data. An important component of such a disc memory is formed by the positioner, i.e. the movable support of the write and/or read transducer (for example, a magnetic head) which is to be accurately positioned over a desired track of the disc as quickly as possible.
Many versions of disc memories are known. A disc memory comprising a device for determining a number of a track of the kind described is known from U.S. Pat. No. 3,812,533. In this disc memory, the radial position of the write/read transducer is controlled by utilizing the servo signals incorporated in a limited number of narrow sectors on each disc. It is thus possible to determine a track number of each track within group of tracks on the disc (so called "coarse" positioning) and, moreover, to realize the accurate positioning over a given track of a group (so-called "fine" positioning). The determination of the track number per group, however, is not sufficient. It must be possible to distinguish each track from all other tracks. The combination of the number of the group of which a track forms part, and the track number within a group form an unambiguous data for the complete address number of the relevant track. Complete positioning of the positioner over a track can be achieved only on this basis. In order to make this possible in the described disc memories without widening the servo sectors (i.e. without loss of effective data storage capacity), there is provided a separate optical position transducer which controls at least the positioning between respective groups of tracks. This separate transducer makes the solution of the positioning problem expensive and requires special structural steps to ensure proper and reliable operation.